Variable condenser and coupling device



June 6, 1933. H, N 1,913,007

VARIABLE CONDENSER AND COUPLING DEVICE Filed Aug. 5, 1927 Patented June 6, 1933 UNITED STATES PATENT OFFICE HAROLD A. SNOW, OF BOON'I'ON, NEW JERSEY, ASSIGNOB, BY KESNE ASSIGNMENTS, TO

RADIO CORPORATION OF AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELA- WARE VARIABLE CONDENSER AND COUPLING DEVICE Application filed August 5, 1927. Serial No. 210,915.

This invention relates to a variable capacity device, or variable condenser, and particularly to a form of said device which is especially adapted for use in coupling electrical circuits; for example circuits employed in radio receiving sets. It relates also to radio receiving sets and circuits, and

to other electrical circuits which embody a device of that form.

For many purposes in the electrical arts it is desirable or necessary to have a variable capacity device which has a high ratio of maximum to minimum capacity. Such a device may be of particular use in the radio art, for example, for use in radio receiving sets or circuits. One instance of this is found in the case of so-called alternating current tubes, that is, audion or vacuum tubes including an anode, one or more control or grid elements, and an electron-emitting cathode which is heated to an emitting temperature by the use of alternating current. When such alternating current tubes are employed in radio receiving sets it is often difiicult to obtain a satisfactory method of volume control, i. e., of varying the amount of amplification according to the strength or" the incoming signal. For various reasons which are well understood it is not desirable or possible to employ the volume control means which are suitable in the case of cathodes which are heamd by direct current.

One of the most satisfactory means of volume control in the case of alternatin current tubes is to employ an additions radio frequency stage having variable coupling with the antenna or other collecting device. This additional stage is preferably an untuned one, since varying its couplin with the antenna would necessitate an individual change in the tuning of this particular stage, and so prevent it from tuning with the other stages of a single-control amplifier, unless a complicated mechanical arrangement were employed.

In addition to the novel variable capacity device referred toahove, my invention, ther fore, relates also to a novel device and circuit arrangement for carrying out a variation in coupling between any two electrical 'mica or the like.

circuits, and more especially between a radio frequency circuit (whether tuned or not), and an antenna or other collecting device. It affords a means for varying the coupling through a very wide range, and in the latter connection gives a practical and efiicient means of volume control, and solves a diflicult problem in connection with the use of alternating current tubes.

The foregoing application of my variable capacity device, while forming an important part of this invention, is only one instance of the many uses to which mydevice may be put in the electrical and radio arts.

In the drawing, Figure 1 shows an arrangement of my variable capacity device employed in connection with a radio receiving set; Figure 2 is another view of a part of the device shown in Figure 1; and, Figure 3 is a diagrammatic representation of one embodiment of the invention as a volume control. lin Fig. 1, a metal base, for example, the frame, subpanel, etc., of the radio receiving set, or part of the main shielding structure thereof, is shown at 1, and is connected to ground. Mounted upon this base is a metal shield, 2, which ma have the form of a box or the like, and w ich. is also grounded. Within the shield 2 is a condenser plate, 3, which is supported by means of the insulation whereby it is kept out of contact with the grounded shield 2.

The condenser plate 3 may 'or may not be covered by an insulating layer or sheet 5, of lit is preferable to employ such insulation to prevent possible short circuit of the condenser. Another condenser plate, '6, is so mounted as to be capable of mechanical movement towards or away from the condenser plate 3. This may suitably he done by means of the movable arm, 'i', having a pivot or fulcrum, 8. The arm 7 may be actuated hy the cam 9 working against any suitable hearing point 10. 'ihe cam 9 may be driven ioy a shaft 11, rotated by a control knob or pulley 12. A spring 8' may serve to lzcep the hearing point it) in contact with the cam 9.

When the condenser plate 6 approaches or recedes f om the condenser plate 3, the effec- Eli tive capacity of the device undergoes a considerable variation, which may be increased by having the plates ver close together (say .002") in the position maximum capacity. 5 In addition to this principal means for varying the capacity, I may employ a secondary or auxiliary means, such as the shielding plate 13, which may be controlled by the movement of the shaft 11, or which may be the subject of independent control.

In the particular arrangement shown, the shielding plate 13 is connected to ound through the shaft 11 and bearing 14, and is operated by the rotation of the shaft. It is so arranged that when the plate 6 closely approaches the plate 3, the shielding late 13 is wholly removed from between t em, but as the plate 6 recedes from the plate 3, the rotation of the shaft 11 operates to interpose the shielding late 13 between the condenser plates 3 an 6. This may occur gradually so as progressively to reduce the effective area of the condenser plates at the same time that the distance between them is increased, the shielding plate being completely interposed when the condenser plates ave this maximum separation. This auxiliary movement may or may not be an automatic one, since I sometimes employ an inde endent control for it.

y the concurrent use of these two means for varying the effective capacity of the device I may obtain a very high ratio of maximum to minimum capacity. In'actual ractice I have readily obtained a ratio 0 the order of 10,000 to 1. I

Figure 2 is another view of a part of the device shown in Fig. 1. The arrow indicates the direction of motion of the shielding plate 13, carried by the shaft 11. The fixe condenser plate 3 18 shown in full, arranged within the shield 2, and the thin insulating sheet 5 is shown as partly broken away to disclose the plate 3. The remainder of the device, except the base 1, is not shown.

It should of course be understood that in the case of other applications of my variable capacity device such elaborate shielding arrangements maybe unnecessary, and various elements shown in Fig. 1 may be omitted.

Figure 3 is a diagrammatic representation of one embodiment of my invention .as a volume control means for a radio receiver. The antenna A is connected to the fixed condenser plate 3, which is surrounded on all but one face by the shield 2. An extension of this shield may be arranged to cover a part of the antenna lead, and prevent stra coupling between this lead and the mova le condenser plate 6. For a similar reason the receiver itself should preferably be shielded as completely as possible. By this arrangement the only path for the transfer of the electrical signal energy from the antenna to the receiving set is between the plates of the variable capacity coupling device itself. The movable shielding plate 13 is here shown partly interposed between the condenser plates 3 and 6, being arranged to move with the shaft 11. The arrows indicate the directions of motion. As the plate 6 recedes, the shielding plate 13 moves further between the plates 3 and 6. The clearance between the movable shielding plate 13 and the fixed shield 2 is preferably made as small as is practical. Both the fixed shield 2 and the movable shielding plate 13 are connected to ground, which may be accomplished as shown in Figure 1, or which may be accomplished by means of connections 16 and 17, as here indicated. The movable condenser plate 6 may be connected to the input circuit of the receiver. Whether this input circuit be tuned or untuned, or is an additional amplifier stage or not, is not material to the present invention. The movable plate is here shown connected to the primary of a coupling transformer T, for generality. It is obvious that the connection to the plates 3 and 6 might be reversed or otherwise varied, according to my invention.

My present invention includes a variable capacity device per se, but its scope is also much broader, since it comprises a novel method and means for coupling any two electrical circuits, when a wide variation in coupling is desired. The invention is moreover es ecially valuable as a method and means or coupling high-frequency electrical circuits, such as those found in radio receiving sets and the like. In such cases the various shielding arrangements herein described may actively cooperate with the other elements of my invention, and constitute an important feature thereof. The wide range of coupling afforded by my invention is another valuable feature thereof. Other bases of my invention have appeared from t e foregoing description.

I claim:

1. In combination a source of signal energy and a utilizing circuit, means for coupling said source to said utilizing circuit comprising a variable capacity device comprising, in combination, a plurality of condenser plates arran ed for relative movement, and a movafile shielding late associated therewith and arranged or interposition between two of said condenser plates for controlling the amount of energy transfer from said source to said utilizing circuit.

2. A variable capacity device comprising, in combination, a control means, a plurality of condenser plates operated by said control means and arranged for relatlve movement from a position of close proximity to a separated position, and a movable shielding plate associated therewith and operated by said control means so .as to be increasingly 4 interposed between said condenser plates as denser plates as'they are they are moved to a separated position, and decreasingly interposed between said conmoved to a position of proximity. r

' '3. A variable capacit device comprising, in combination, a fixe condenser plate, a movable condenser plate, a shaft for controlling the movement of said second condenser plate, and a shielding plate operated by said shaft and arrange to be increasingly interposed between said fixed and movable condenser plates as the distance between them is increased.

4. A variable capacity device for use at high frequencies, comprising, in combination, a plurality of condenser plates arranged for relative movement, a grounded creasing their efiective exposed surface as" shield for one of said condenser plates, and a grounded movable shielding plate arranged for interposition between said shielded condenser plates and another condenser plate.

5. Method of obtaining a high ratio of maximum to minimum capacity, which comprises varying the separation between two condenser plates, and simultaneously detheir separation increases and increasing their GfiBCtlVE exposed surface as their separation decreases While malntalning each plate substantially in a position which is the projection of the other for all degrees of separation of the two plates.

6. The steps in a method of obtaining a high ratio of maximum to minimum direct capacity between two condenser plates or the like which comprise varying the separation between said two plates and simulta-- neously decreasing their effective exposed surface as their se aration increases and increasing their e ective exposed surface as their separation decreases while maintaining each plate substantially in a position which is the projection of the other for all degrees of separation of the two plates.

In testimony whereof, I affix my signature.

HAROLD A. SNOW. 

